1. Field of the Invention
The present invention relates to a method of lining pipes for supplying gases, water, etc., especially pipes having branches.
2. Description of the Prior Art
Piping systems comprising a large-diameter pipe (hereinafter referred to as "large pipe") and a small-diameter pipe (hereinafter referred to as "small pipe") are lined usually after the pipes are separated by cutting at the branch point to line them individually. This method requires much labor for the separation and for rejoining the lined pipes and is very inefficient. In view of this, a method has recently been proposed by which the large pipe and the small pipe can be lined efficiently as joined together without separation.
This method comprises the step of lining a small pipe by causing a small-diameter running body corresponding thereto to run through the pipe, and the step of lining a large pipe by causing a large-diameter running body corresponding thereto to run through the pipe, one of the two steps being performed before the other. However, since the lining or seal composition is partly forced into the small pipe during the large pipe lining step, the method has the problem that the excess of the seal composition must be pushed back and thereafter discharged from the large pipe.
In the case where this method is practiced for a piping including a large number of small pipes as branches, the excesses of the seal composition pushed back or returned will amount to a considerable quantity when combined. Economically it is very disadvantageous to discharge and discard the whole quantity in view of the waste of the composition and the procedure needed for the disposal. Moreover, the seal composition returned from the small pipe at an upstream location is likely to flow into another small pipe at a downstream location. To avoid this problem, there is the need to limit the length of lining which can be formed by a single pass, or the return and discharge of the excess must be repeated. Such an attempt nevertheless inherently imposes a limitation on the improvement of efficiency.